Metal punching

ABSTRACT

A PUNCH PRODUCES AN INDENTATION IN THE METAL WITH SOME OF THE METAL BEING DISPLACED OUTWARDLY ON THE OPPOSITE SIDE. THIS DISPLACED METAL IS REMOVED AND A PUNCH IS INSERTED INTO THE IDENTATION AND FORCED THROUGH THE METAL.   D R A W I N G

' Marc 2, 1971 J. E. FULLI E R 3,566,513

' 'METAL PUNCHING I Filed March 5, 1969 JucZs'OTQEQu /Zr r Patented Mar.2, 1971 3,566,513 METAL PUNCHING Judson E. Fuller, River Forest, 111.,assignor to The Harrington & King Perforating Co., Inc., Chicago, Ill.Filed Mar. 5, 1969, Ser. No. 804,390 Int. Cl. B23p 13/04 US. Cl. 29-5574 Claims ABSTRACT OF THE DISCLOSURE A punch produces an indentation inthe metal with some of the metal being displaced outwardly on theopposite side. This displaced metal is removed and a punch is insertedinto the indentation and forced through the metal.

BACKGROUND OF THE INVENTION It is not diflicult to punch a relativelysmall hole, e.g., one-sixteenth of an inch, in sheets of comparativelysoft metal, provided that the thickness of the metal is no more thanabout the diameter of the punch. However, some metals, e.g., stainlesssteel, ofier such a high resistance to a punching operation that it isexceedingly diflicult to consistently form holes by punching in suchmetals. For example, some companies that commercially form perforatemetal by punching will limit their operations on stainless steel toholes which are no smaller than twice the thickness of the metal. Forexample, they would not consider perforating metal with one-sixteenthinch diameter holes in a sheet of stainless steel of greater thickness.

The difficulty is that there is so much resistance to the movement ofthe punch through the metal that the punches tend to break. Even thougha few holes might be formed, the punches will break before very many arecompleted and it is uneconomical to have to keep replacing punches.

In certain industries there is a demand for perforate metal, e.g.,filtration screens, with the requirements, for example, calling forone-sixteenth inch holes in a sheet of stainless steel approximatelythree-sixteenths of an inch thick. Since the companies which formperforate metal by punching refuse to undertake such an operation, themetal must be formed by an operation such as drilling or milling (whereslots are acceptable). These are extremely expensive procedures ascompared to punching.

The principal object of the present invention is to provide a novelmethod for punching of metals which can be performed Without the extremedanger of breaking punches.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view illustratingdiagrammatically the first step of the disclosed method;

FIG. 2 is an elevational view illustrating diagrammatically the secondstep of the disclosed method; and

FIG. 3 is a sectional elevational view illustrating the third step ofthe disclosed method.

DESCRIPTION OF SPECIFIC EMBODIMENT The following disclosure is offeredfor public dissemination in return for the grant of a patent. Althoughit is detailed to ensure adequacy and aid understanding, this is notintended to prejudice that purpose of a patent which is to cover eachnew inventive concept therein no matter how others may later disguise itby variations in form or additions or further improvements. The claimsat the end hereof are intended as the chief aid toward this purpose; asit is these that meet the requirement of pointing out the parts,improvements, or combinations in which the inventive concepts are found.

FIG. 1 illustrates a sheet of stainless steel in which holes are to bemade to form a perforate sheet. It is, for example, three-sixteenths ofan inch thick. The sheet is run through a punching machine of which onlythe punches and their associated dies are illustrated. The punches 11are each aligned with an opening 12 in a platen or die 13. The punches11 have a comparatively round nose with the sides of the punch having aslight taper. The openings 12 are substantially larger in diameter thanis the cross-sectional diameter of punches 11. Thus, for example, thepunches 11 have a nominal cross-sectional diameter of one-sixteenth ofan inch, while the cross-sectional diameter of holes 12 isthree-sixteenths of an inch. The nose of each punch 11 is, of course, injuxtaposition to one face 10a of the sheet 10, while the other face 10bis placed against die 13.

The punches 11 are forced (by other portions, not shown, of the punchpress) against and into the sheet 10 at face 10a so as to produceindentations 15. The depth of the indentation will vary with theconditions encountered, e.g., the diameter of the hole to be formed, thethickness of the sheet, the resistance that the sheet offers, etc. Inthe illustration given, the depth of the indentation 15 is in the rangeof approximately one-half to two-thirds the thickness of the sheet 10between faces 10a and 10b. In any event, it should be sufliciently deepso that some of the material of the sheet is forced downwardly intoopenings 12 to form significant protrusions 16. Under the specificconditions given, these protrusions 16 extend approximatelyone-sixteenth of an inch beyond face 10b of the sheet.

The second step of the process is to remove the protrusion 16. This caneasily be done with a surface grinder. FIG. 2 illustrates the removal ofthe protrusion 16 by a rotating grinding wheel 17, with the protrusionto the left of the wheel having been removed.

Following the removal of the protrusion 16, a second punching operationis performed as illustrated in FIG. 3. Here there is a punch 19 which isaligned with opening 20 in a die 21. The sheet 10 is positioned so thatthe indentations 15 are successively aligned with punch 19 and opening20. Punch 19 is then inserted into the indentation 15 and forced onthrough the sheet 10 so as to eject a slug of metal 22 to leave afinished hole 23 in the metal at the point at which the indentation 15was first formed.

In the drawings the punches 19 are illustrated as being substantiallylonger than are the punches 11. This may be desirable in some instancesinasmuch as the shorter punches are in less danger of breakage. Thus,the punches 11 need be no longer than substantially the desired depth ofthe indanta-tions 15. The cleanout punches 19, however, must ofnecessity be sufiiciently long to insure the removal of slug 22 from themetal. However, some practitioners of the present method may desire notto use two sets of punches and will use punches 19 for the first step aswell as for the third step.

Another modification that some perforators may desire to use,particularly when the sheet 10 is of a metal that is very tough and theholes 23 are to be of a relatively small diameter in relation to thethickness of the sheet 10, is to repeat the first two steps severaltimes before carrying out the third step. That is, a small indentationis made with a correspondingly small amount of metal being extruded onthe back side in the form of a protrusion 16. This protrusion is groundoff. Thereafter the indentation 15 is deepened by a second punchingoperation, followed by a second grinding operation to remove theresulting protrusions. Only thereafter is the final punching operationof FIG. 3 carried out. Also in the illustrated embodiment the opening 20in die 21 are substantially equal in diameter to the punch diameter,with only a small clearance for the punch 19 and slug 22 being providedin the opening 20. Larger diameter openings 20 can be employed if theultimate user of the sheet 10 can stand for (or desires) some deformingof the face 1% about the finished openings,

I claim:

1. In the method of punching a hole in a metal sheet using a punch onone side of the metal and a die having a punch opening aligned with thepunch on the other side of the sheet, the improvement comprising thesteps of:

first, pressing said punch into the sheet sufliciently far to form anindentation in said one side and displace some metal from the sheetoutwardly from said other side of the sheet, but not sufliciently far toextend through the sheet nor to remove a slug of metal from the sheet;

thereafter, removing said displaced metal down to about the level ofsaid other side; and

thereafter, continuing to press the punch against the sheet in saidindentation to force a hole in the metal.

2. In the method of claim 1, performed on a sheet of stainless steel,wherein at the end of the first step the punch has penetrated into thesheet in the range of ap- References Cited UNITED STATES PATENTS2,182,067 12/1939 Bruecker 72379X 2,540,852 2/ 1951 Wilcox 29557X3,232,156 2/1966 Fuller 8339 JOHN F. CAMPBELL, Primary Examiner V. A. DIPALMA, Assistant Examiner US. Cl. X.R. 8339, 52

